RS-232C

What is RS-232C?

It is one of the serial interface standards for communicating between devices established by the Electronic Industries Alliance (IEA) in the United States.

Signal level

RS-232C sends signals using 0 (space) and 1 (mark).

The voltage level is 0 for +3 to + 15V and 1 for -3 to -15V.

Standard, method

Cable length	Transmission speed	Number of connectable units	I/O methods
15m or less	20kbps	1 : 1	Unbalanced type (single-ended)

Unbalanced (single-ended): A single signal line is used to represent a signal by the potential difference from ground. Compared to balanced RS-422, it is more susceptible to noise and cannot be used for long-distance, high-speed communication.

The connector is specified to use D-SUB 25 pin or D-SUB 9 pin, and the pin arrangement is specified as follows.

Pin arrangement 25 pins

Pin No.	Signal name	I/O	Content(original standard)
1	N.C (FG)	-	Not connected（Housing GND）
2	TxD	OUT	Transmission data
3	RxD	IN	Reception data
4	RTS	OUT	Transmission request
5	CTS	IN	Transmission possible
6	DSR	IN	Data set ready
7	GND	-	Ground
8	DCD	IN	Carrier detection
9	N.C	-	Not connected
10	N.C	-	Not connected
11	N.C	-	Not connected
12	N.C	-	Not connected
13	N.C	-	Not connected
14	N.C	-	Not connected
15	N.C	-	Not connected
16	N.C	-	Not connected
17	N.C	-	Not connected
18	N.C	-	Not connected
19	N.C	-	Not connected
20	DTR	OUT	Data ready
21	N.C	-	Not connected
22	RI	IN	Called indicator
23	N.C	-	Not connected
24	N.C	-	Not connected
25	N.C	-	Not connected

Pin arrangement 9 pins

Pin No.	Signal name	Alias	I/O	Contents
1	DCD	CD	IN	Carrier detection
2	RxD	RD	IN	Reception data
3	TxD	SD	OUT	Transmitted data
4	DTR	ER	OUT	Data terminal ready
5	GND	SG	-	Ground
6	DSR	DR	IN	Data set ready
7	RTS	RS	OUT	Transmission request
8	CTS	CS	IN	Transmission possible
9	RI	CI	IN	Called indicator